Non-isotropic shadow effect with various pattern direction in anamorphic high numerical aperture system

Abstract

Even though EUV lithography has extremely short wavelength source, a high numerical aperture(NA) system larger than 0.5 is required to make fine pattern of 1X nm and below. In order to avoid reflective efficiency loss and increase of chief ray angle of incident light, anamorphic high NA is suggested. Suggested anamorphic NA system has non-isotropic magnification which is varied 4X to 8X and the mask NA shape is ellipse due to non-isotropic magnification distribution. Anamorphic NA system has a non-conventional shadow effect due to non-isotropic incident angle distribution and magnification. These non-isotropic characteristics leads the reduction of asymmetric shadow distribution and it involves the reduction of horizontal-vertical bias. As a result anamorphic NA system can achieve balanced patterning results regardless of pattern direction and incident direction.